Chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) have been used commonly in a wide variety of solvent applications such as drying, cleaning (e.g., the removal of flux residues from printed circuit boards), and vapor degreasing. CFCs and HCFCs also commonly have been used as physical blowing agents to generate cells in foamed plastic materials. However, CFCs and HCFCs have been linked to the destruction of the earth's protective ozone layer, and replacements have been sought. The characteristics sought in replacements, in addition to low ozone depletion potential, typically have included low boiling point, low flammability, and low toxicity. Solvent replacements also should have a high solvent power.
It is known that azeotropes possess some properties that make them useful solvents. For example, azeotropes have a constant boiling point, which avoids boiling temperature drift during processing and use. In addition, when a volume of an azeotrope is used as a solvent, the properties of the solvent remain constant because the composition of the solvent does not change. Azeotropes that are used as solvents also can be recovered conveniently by distillation.
A number of examples of azeotropic, and azeotrope-like, compositions that include a perfluorinated compound and an organic solvent are known in the art.
Zuber, U.S. Pat. No. 4,169,807 describes an azeotropic composition containing water, isopropanol, and either perfluoro-2-butyltetrahydrofuran or perfluoro-1,4-dimethylcyclohexane. The inventor states that the composition is useful as a vapor phase drying agent.
Van der Puy, U.S. Pat. No. 5,091,104, describes an "azeotropic-like" composition containing t-butyl-2,2,2-trifluoroethyl ether and perfluoromethylcyclohexane. The inventor states that the composition is useful for cleaning and degreasing applications.
Fozzard, U.S. Pat. No. 4,092,257 describes an azeotrope containing perfluoro-n-heptane and toluene.
Batt et al., U.S. Pat. No. 4,971,716 describes an "azeotrope-like" composition containing perfluorocyclobutane and ethylene oxide. The inventor states that the composition is useful as a sterilizing gas.
Shottle et al., U.S. Pat. No. 5,129,997 describes an azeotrope containing perfluorocyclobutane and chlorotetrafluorethane.
Merchant, U.S. Pat. No. 4,994,202 describes an azeotrope containing perfluoro-1,2-dimethylcyclobutane and either 1,1-dichloro-1-fluoroethane or dichlorotrifluoroethane. The inventor states that the azeotrope is useful in solvent cleaning applications and as blowing agents. The inventor also notes that "as is recognized in the art, it is not possible to predict the formation of azeotropes. This fact obviously complicates the search for new azeotrope compositions" (col. 3, lines 9-13).
Azeotropes including perfluorohexane and hexane, perfluoropentane and pentane, and perfluoroheptane and heptane are also known.
There currently is a need for alternative azeotrope compositions that can be used in solvent and other applications. Preferably these compositions would be non-flammable, have good solvent power, and cause little, if any, damage to the ozone layer. Preferably, also, the azeotrope composition would consist of readily available and inexpensive solvents.